add a test for using cache_directories option in package.json

test/fixtures/cache-directories/README.md

+A fake README, to keep npm from polluting stderr.
\ No newline at end of file

test/fixtures/cache-directories/bower.json

+{
+  "name": "node-buildpack-test-app",
+  "dependencies": {
+    "jquery": "^1.11.1"
+  }
+}

test/fixtures/cache-directories/package.json

+{
+  "name": "node-buildpack-test-app",
+  "version": "0.0.1",
+  "description": "node buildpack integration test app",
+  "repository" : {
+    "type" : "git",
+    "url" : "http://github.com/example/example.git"
+  },
+  "engines": {
+    "node": "0.10.18"
+  },
+  "dependencies": {
+    "bower": "1.3.12"
+  },
+  "scripts": {
+    "postinstall": "bower install --allow-root"
+  },
+  "cache_directories": ["bower_components", "node_modules"]
+}

test/run

@@ -172,6 +172,18 @@ testBuildWithCache() {
   assertCapturedSuccess
 }
 
+testBuildWithUserCacheDirectories() {
+  cache=$(mktmpdir)
+  compile "cache-directories" $cache
+  assertCapturedSuccess
+  assertEquals "1" "$(ls -1 $cache/node | grep bower_components | wc -l)"
+  assertEquals "1" "$(ls -1 $cache/node | grep node_modules | wc -l)"
+
+  compile "cache-directories" $cache
+  assertCaptured "Loading user cache directory from cache: bower_components"
+  assertCapturedSuccess
+}
+
 testModulesCheckedIn() {
   compile "modules-checked-in"
   assertCaptured "node_modules source: prebuilt"